Your Pentax K1000 used a focal plane shutter; two rubberized cloth curtains swept horizonally across the film; the first curtain opened exposing the film and then after the proper time the second curtain followed it, ending the exposure.
What I think you feel may be cracks are instead the "leaves" of a leaf shutter. Made of very thin steel, they swing into the shutter body simultaneously, allowing light to strike the film. After the proper time they return to their original position to close the lens to light. If either type of shutter is working properly you can hear a clockwork mechanism buzzing when the shutter is operated and, looking through the open back toward the lens, see the shutter open and then close.
Shutters of either type generally first indicate problems, by slow speeds being waaaay too slow. Such problems can usually be fixed, although the cost may be worth more than the camera. A Zeiss camera may well be worth the cost of a Clean Lubricate and Adjust, aka CLA. Zeiss cameras were generally well thought of. Google Zeiss Contina ii and you will note that there are TWO Contina ii; one a folding rangefinder the other fixed lens. Note that the Tessar lens is more desireable than the Novar optic. My guess is that the folding model is more desireable, at least it would be to me. Many of the non-folders have a built in light meter, after the passage of so many years the readings from it are probably unreliable. If so look for a good used meter; many can be found here at Photrio.
Good luck!
